A portable power tool can be adaptable, e.g., for use as a disk cutter or a chain saw. A power source such as a small-scale air-cooled two-stroke gasoline engine or an electrical motor or the like is disposed in a power unit of the power tool. Typically, the power unit has a handle and the like which can serve equally for either adaptation, e.g., whether a disk cutter or a chain saw assembly is attached to the power unit. But there are differences in the way power is transmitted from the power unit to different tool assemblies: in the case of an attached disk cutter assembly, power is transmitted typically by a pulley and belt drive; in the case of a chain saw, by a sprocket wheel directly to the saw chain.
Conventionally, to change the function of such a power tool from cutting to sawing for example, a cutter assembly including a cutting disk or blade, a protective blade cover, and a supporting arm and the like is removed from the power unit. Then the pulley is removed from the power output or drive shaft of the power source, a sprocket wheel is put in place, and a chain saw assembly is attached to the power unit. Changing back to cutting involves a corresponding inverse procedure.
These procedures are cumbersome and time consuming especially when, as is typical, a centrifugal clutch is included for transmission of power from the drive shaft. The drawbacks are serious especially in an emergency, e.g., in rescuing an earthquake victim trapped under a house.